1. Field of the Invention
The present invention relates to AD converting circuits, photoelectric converting apparatuses using them, image pickup systems, and driving methods for AD converting circuits. In particular, it relates to one configured to AD convert an input signal by performing an operation of comparing a gradually changing reference signal and the input signal a plurality of number of times.
2. Description of the Related Art
Solid-state image pickup devices have often been used in digital cameras and digital videos. A solid-state image pickup device has, on one chip, a plurality of pixels and a plurality of AD converting circuits which convert analog signals output from the plurality of pixels to digital signals. Several techniques have been proposed for the architectures of the AD converting circuits.
Japanese Patent Laid-Open No. 2004-304413 performs N-bit AD conversion on analog signals output from pixels, amplifies the residual signals, and then performs M-bit AD conversion on the amplified residual signal. The AD conversion in two stages allows AD conversion of (N+M) bit resolution.
However, the configuration of Japanese Patent Laid-Open No. 2004-304413 has a problem of an increase of the circuit scale because separate AD converting circuits are provided for the AD conversions of the first stage and the second stage.